1. Technical Field of the Invention
The present invention relates to the photostabilization towards UV radiation of screening systems comprising at least one dibenzoylmethane derivative. The invention also relates to novel compositions, in particular cosmetic compositions for topical application.
2. Description of Background/Related/Prior Art
With the aim of ensuring protection of the skin and keratin materials against UV radiation, antisun compositions comprising UV-A-active and UV-B-active organic screening agents are generally used. The majority of these screening agents are liposoluble.
In this regard, one family of screening agents that is particularly advantageous currently consists of dibenzoylmethane derivatives, and especially 4-(tert-butyl)-4′-methoxydibenzoylmethane, which show high intrinsic absorbing power. These dibenzoylmethane derivatives are products that are already known as UV-A-active screening agents and are described especially in FR-A-2,326,405 and FR-A-2,440,933, and also in EP-A-0,114,607. 4-(tert-Butyl)-4′-methoxydibenzoyl-methane is moreover currently sold under the trademark “PARSOL 1789” by Hoffmann LaRoche.
However, these screening agents, and especially Parsol® 1789, or butylmethoxydibenzoylmethane (INCI name) are products that are relatively sensitive to ultraviolet radiation, i.e., they show a tendency to degrade under the action of this radiation. Thus, this lack of photochemical stability of sunscreens in the face of ultraviolet radiation, to which they are by nature intended to be subjected, does not make it possible to ensure constant protection over prolonged exposure to the sun, such that, in a restricting manner, repeated applications at regular and close intervals must be performed by the user in order to obtain effective protection of the skin against UV rays.
It is known practice to combine sunscreens with certain compounds in order to improve their photostability. Thus, EP-1,093,797 describes a process for improving the stability of at least one dibenzoylmethane derivative towards UV radiation, which entails combining the dibenzoylmethane derivative with an insoluble organic screening agent in micronized form, the mean particle size of which ranges from 0.01 to 2 μm.
EP-0,982,310 describes a process for photostabilizing a dibenzoylmethane derivative with a silane or organosilane compound containing a 2-hydroxy-benzophenone function.
EP-1,043,966 describes a process for photostabilizing a 1,3,5-triazine-based sunscreen with an ethylenically unsaturated compound.
EP-1,096,916 describes a process for photostabilizing a dibenzoylmethane derivative with an amphiphilic thickening copolymer which is not of block type.
However, the sunscreens thus stabilized show insufficient resistance to degradation by UV radiation, and the photostabilization of photosensitive sunscreens towards UV radiation is, at the present time, still a problem that has not yet been solved entirely satisfactorily.